Method of rendering galvanic cells leakproof by encasing them in a jacket of thermoplastic synthetic material



Dec. 1, 1970 J. MuslL. 3,544,386

METHOD OF RENDERING GALVANIC CELLS LEAKPROOF BY ENCASING THEM IN A JACKET OF THERMOPLASTIC SYNTHETIC MATERIAL INVENTOR BY WMM-@J9 ATTORNEY.

J. Musn. n 3,544,385 METHOD OF RENDERING GALVANIC CELLS LEAKPROOF BY ENCASING Dec. 1, 1970 THEM IN A JACKET OF' THERMOPLASTIC SYNTHETIC MATERIAL 2 Sheets-Sheet z Filed March 6, 1968 INVENTOR z Ja/:n M1151! ATTORNEY.

United States Patent O "ice 3,544,386 METHOD OF RENDERING GALVANIC CELLS LEAKPROOF BY ENCASING THEM IN A JACKET OF THERMOPLASTIC SYNTHETIC MATERIAL Johann Musil, Vienna, Austria, assignor to Telephonund Telegraphen-Fabriks-Aktiengesellschaft Kapsch & Soehne, Vienna, Austria, a corporation of Austria Filed Mar. 6, 1968, Ser. No. 710,817 Claims priority, application Austria, Mar. 7, 1967, A 2,173/67, Patent 269,242 Int. Cl. H01m 1/02 U.S. Cl. 136-175 5 Claims ABSTRACT OF THE DISCLOSURE Method of rendering galvanic cells leakproof by inserting them in a plastic tubular jacket closed at one end by a iirst end wall. A second plastic end wall is inserted into the terminal portion of the tubular jacket, and pressure is exerted on the outside of the second-end wall which is transmitted by way of the cell to the opposite, iirst end wall as a deforming pressure arching the iirst end wall elastically outwardly. The tubular jacket is welded to the second end wall, and the welded-on-wall is relieved of pressure. By the elastic return to its original shape of the second end wall, there is produced a contact pressure between the cell contacts and external contacts embedded in said two end walls.

Reference is made to the co-pending patent application of Ernst Karobath, Ser. No. 641,572, tiled May 22, 1967 for Galvanic Primary Cell, now Pat. No. 3,501,351 dated Mar. 17, 1970, which application has been assigned to the assignee of the instant application.

Galvanic primary cells (for example Leclanch cells) so constructed as a rule that the negative electrode is of pot or can form (zinc can) and forms the container of the cell. The can surrounds the positive electrode (carbon electrode) with the depolarizer composition and the electrolyte. The electrical energy is produced by decomposition of the negative electrode. During discharge, water is simultaneously formed and results in liquefaction of the electrolyte, this being solidified by means of a swelling substance in the unused state of the galvanic or voltaic cells. The result of this liquefaction is a leakage of electrolytic liquid through the can wall, which is gradually destroyed during discharge. This leakage of the electrolytic liquid often causes great damage in the devices in which the primary cells are installed.

There have already been proposed numerous methods of constructing cells the aim of which is to prevent the escape of liquid from the cells during and after discharge, but it has not really been possible to solve this problem up to now.

So-called leakproof cells, which are enclosed in a jacket of absorbent material over which another, outer, jacket generally consisting of sheet steel is applied with the use of pressure, the outer steel jacket being connected to the top and the bottom of the cell by rolling them up under pressure, do not provide a satisfactory solution, because in these cells corrosion phenomena occur at both poles and result in the cell developing leaks at the external contacts.

The use of a leakproof plastics jacket has heretofore been a failure because the external metal contacts (top and bottom contacts) which are required for connection to the poles of the cell could not be passed through a plastics jacket in liquid-tight relationship. In fact, if a metal part is embedded in thermoplastic synthetic material Patented Dec. 1, 1970 by injection moulding, the plastic shrinks on solidiiication, as a result of which the plastics material lifts away from the embedded metal part and moves towards the greatest accumulation of plastics material. A narrow gap is thereby formed between the plastic and the metal and the consequence of this is a leak. It has been possible to overcome the diiculties described by means of earlier proposals made by the applicants, according to which leakproof ernbedding of the external contacts in the top and bottom of a plastics jacket can be achieved in that the external contacts both in the bottom and in the top are formed by sheet metal parts which, extending through the top and bottom, respectively, are embedded all round in the plastic and, for sealing purposes in the embedding zone, have a row of closely adjacent apertures which extends over the whole of the said embedding zone, the said apertures having plastic which shrinks on solidication extending through them in rivet fashion, as a result of which the sealing surfaces are twisted tightly against one another. The length over which each of the sheet metal parts is embedded, measured from the outside to the inside of the top or bottom, is preferably substantially greater than the thickness of the sheet metal parts in the embedding zone, so as also to prevent any electrochemical corrosion of the external contacts. According to the said earlier proposals made by the applicants, the enclosing Wall of the outer jacket preferably consists of a soft plastic which is permeable to gas, but liquid-tight, for example high-pressure polyethylene, whereas the top and bottom of the jacket consist of a hard thermoplastic which is gas-tight and liquid-tight, for example low-pressure polyethylene. The top and bottom may be united with the enclosing wall of the jacket to form tight joints therewith by injection moulding, welding and/ or melting. In other earlier applications, the applicants have also indicated methods and devices which enable the plastics top and/or bottom to be Welded in leakproof manner to the thin plastics enclosing wall.

The present invention relates to a particularly advantageous method of rendering galvanic cells leakproof by encasing them in a jacket of thermoplastic synthetic material which permits the application of all the above-described earlier proposals made by the applicants and ensures that after the cell or a stack of cells has been encased the external contacts in the top and bottom bear against the associated cell contacts with considerable pressure and thus ensure a satisfactory transfer of current.

The method according to the invention consists in that a tubular jacket of thermoplastic synthetic material which is closed at one end by an end wall in which an external contact is embedded, and into which a galvanic cell or a stack of cells has been so inserted that one cell contact is touching the external contact in the end Wall, is supported at the peripheral edge of this end wall, after which a second end wall of thermoplastic synthetic material in which an external contact is likewise embedded is so inserted into the terminal portion of the tubular jacket projecting beyond the cell or the stack of cells that the external contact of the said second end wall likewise comes into contact with a cell contact, that on the outside of the second end wall there is then exerted a pressure slightly displacing this wall in the terminal portion of the tubular jacket, the said pressure being transmitted by way of the cell or the stack of cells in the tubular jacket to the opposite end wall supported at its edge as a deforming pressure arching the last-mentioned end rwall outwards elastically, and that the terminal portion of the tubularjacket is then 'welded to the adjoining second end wall by the action of heat and pressure, the welding zone is thereafter cooled and, finally, after the welding zone has solidified, the top of the welded-on end wall is relieved of the pressure, so that by elastic return to 3 shape of the other end wall a considerable contact pressure is produced between the cell contacts and the external contacts embedded in the two end walls.

An apparatus according to the invention which is suitable for performing this method is essentially characterised in that an axially movable pressure ram is arranged in axial alignment with respect to an annular bearing zone for the peripheral edge of one end of the cell assembly, the annular bearing zone being formed by a supporting element for the cell assembly, and a cap-like welding mould movable axially independently of the pressure ram and which can be heated and preferably also cooled and has an opening for the pressure ram is arranged coaxially therewith, so that after that end 'wall which is to be lwelded on has been forced down by means of the pressure ram and the other end wall of the jacket has been thereby caused to arch outward elastical-` ly, the Welding mould can be placed over the peripheries of the enclosing wall and the end wall of the jacket Iwhich is to be welded on, the Welding mould overlapping the said peripheries.

An embodiment of the invention will now be described more fully with reference to the drawings, FIGS. 1 to 3 illustrate diagrammatically an apparatus according to the invention in three different working stages. FIGS. 4 and 5 illustrate the working procedure and the locking of the pressure ram of the apparatus according to the invention.

In the example shown, the cell assembly designated as a whole -by the reference X consists of a single galvanic cell Z, the bottom contact B of which is formed by the base surface of a zinc can and the top contact K of which is formed by the free end of the carbon electrode.-The complete cell is enclosed in a jacket consisting of a cylindrical surrounding or sheathing wall M, preferably of high-pressure polyethylene, an end Wall S1 already united lwith this surrounding wall and containing an external contact A1 embedded therein in a leakproof manner, and an end wall S2 to be welded on by means of the apparatus according to the invention and in which an external contact A2 is likewise embedded in a leakproof manner. The external contact A1 establishes the conductive connection with the top contact K and the external contact A2 establishes the conductive connection with the bottom contact surface B ofthe cell Z. For leakproof embedding of the contacts A1 and `A2 in the plastics material of the end walls S1 and S2, which preferably consists of low-pressure polyethylene, the contact plates, as` already mentioned, are provided in accordance .'with an earlier proposal with a complete vrow of closely adjacent apertures in the embedding zone, these apertures having plastic extending through them in rivet fashion.

The assembly described, in which the end wall S2 is inserted loosely into the terminal portion of the surrounding Wall M, is held Iby a supporting element 1 of the apparatus according to the invention, this supporting element having an axial cylindrical opening 2 adapted to the contour of the cell assembly and merging into a narrower opening 4 by way of a shoulder forming an annular bearing surface 3 for the peripheral edge of the end wall S1 of the cell jacket.

Above the cell assembly X supported on the annular bearing surface is an axially movable pressure ram 5 which is controlled by a hydraulic cylinder 6 and extends through the cylinder, the free endof the ram 5 carrying a wedge 7. As will be described hereinafter, this wedge 7 can co-operate with a sliding wedge v8 actuated n turn duct 13. 'I'he mould 10 has projecting arms which areconnected to the lower endsof actuating rods 14. The upper ends of the actuating rods 14 are interconnected by a crossbeam 15 and a drive in the form of a pneumatic cylinder 16 acts on this crossbeam. Arranged coaxially with the ram 5 and the mould 10 is an annular heating body 17 which carries a heat shield 18 on top and can be moved past the pneumatic cylinder .6 of the pressure ram 5 and is carried by rods 19 which are also interconnected at their upper ends by a crossbeam 20 on which a drive in the form of a pneumatic cylinder 21 acts. The actuating rods 19 are passed through bores in the crossbeam 15 joining the actuating rods 14.

The welding mould 10 is thin-walled and consists of material which is as good a heat conductor as possible. The mould is normally cooled to far below the softening point of the plastic by a constant flow of cooling medium through the duct 13. By placing the heating body 17 which is fed with electricity, for example, and has great heat capacity on the thin-Walled welding mould 10, which has a small heat capacity, the region of the neck 12a of the cap-like mould, in which the welding of the surrounding wall M to the end wall S2 of the cell assembly X is to take place under the action of heat and pressure, can be rapidly heated to welding temperature and the cooling elfectovercome. After the heating body 17 has been lifted away from the mould .10, the mould again rapidly assumes the temperature of the cooling medium, which is substantially below the softening point of the plastic.

In the initial position shown in FIG. 1, the pressure ram 5, the mould 10 and the heating body 17 are in the raised, inoperative position. After the lprepared cell assembly X has been inserted in the opening 2 in the supporting element 1, the pressure ram 5 is lirst lowered by applying a constant predetermined pressure in the pneumatic cylinder 6, so that the ram shifts the end wall S2 slightly within the surrounding wall and, by way of the cell Z and its top contact K supported against the external contact A1 of the end wall S1, exerts a deforming pressure on the end wall S1 supported only at its peripheral edge on the annular bearing zone 3 of the supporting element 1. In this way, the said end wall S1 is archedoutward elastically, as shown in FIGS. 2 to 4. The effective elastic deforming pressure has a constant predetermined value. The pressure ram 5 is now held by supplying the pneumatic cylinder 9 and thereby causing the sliding wedge 8 to advance until it bears against the wedge 7 connected to the pressure ram 5, so that the wedge 7 cannot move downwards any further, that is the elastic outward arching of the end wall S1 is not altered during the further working stages.

After this first working stage, pressure is applied in the pneumatic cylinder 21, as a result of which the heating body 17 is placed on the mould 10 by means of the crossbeam 20 and the actuating rods 1,9, so that the mould rapidly absorbs heat from the heating body and is moved downward while it is being heated until it overlaps with its cap-like cavity the upper edge of the surrounding wall M and the end Wall S2 of the cell jacket and heats the abutment area of these two parts to welding temperature. The forward movement of the welding mould is limited, however, owing to the fact thatvthe cross beam 15 to which the welding mould 10 is attached by means of the actuating rods y14 abuts against the .wedge 7 retainedk by the sliding wedge 8. This limitation of travel ensures that,`

irrespective of slight variations in the height of the cell assembly X in consequence of manufacturing tolerances, the distance of advance of the welding mould 10 in rela` tion to the cell assembly X is always constant. The welding zone is shaped by the suitably rounded hollow neck 12a of the welding mould 10. v

In FIG. 2, the pressure ram 5, the welding mould 10 and the heating body 17 are shown in the position adopted by these` parts during the welding operation.

After this 'welding operation, the heating body 17 is lifted away from the welding mould by applying pressure in the cylinder 21, so that the said mould is cooled down below the solidication temperature of the plastic and the welding zone is consequently rapidly solidied. This working stage is shown in FIG. 3. After solidii'lcation of the welding zone, the Welding mould is lifted away by applying pressure in the cylinder 16 and, finally, by applying pressure in the cylinder 6 the pressure ram 5 is retracted, as a result of which the end wall S2 is relieved of pressure and the elastically arched end Wall S1 assumes its original form, a relatively high contact pressure ensuring a good transfer of current being produced between the external contacts A1 and A2 and the associated cell contacts K and B, respectively. By applying pressure in the cylinder 9, the sliding wedge 8 is then retracted andthe finished encased cell is removed from the supporting element 1, after which the apparatus is ready for the next operating cycle.

Of course, the apparatus described allows various modications of design within the limits of the invention. Thus, it is also possible to employ other driving means in place of the pneumatic cylinders 6, 9, 16 and 21 illustrated. Instead of a continuously cooled welding mould 10, the cooling eiect of which is temporarily overcome by placing a heating body 17 of high heat capacity thereon in order to bring the Welding mould to welding temperature, it is also possible to use a mould consisting of material which is a good conductor in the welding zone and of heat-insulating material in the adjacent zones and on which heating and cooling bodies of high capacity are placed alternately. It is also possible to employ a -welding mould which is heated directly, for example by highfrequency currents. The actuating members for the main parts of the apparatus, such as the pressure ram 5, the welding mould 10 and the heating body 17, may also be controlled otherwise than through rods 14, 19, etc., for instance through cam discs. The locking device for the pressure ram and the stop for the travel of advance of the welding mould may also be designed otherwise than shown.

What I claim is:

1. In a method of rendering galvanic cell means leakproof by encasing in a jacket of thermoplastic synthetic material closed at one end by an end wall bearing a rst external contact; the steps comprising:

inserting a galvanic cell means having cell contacts into said jacket whereby said rst external contact is touching one cell contact,

inserting into said jacket a second end wall of thermoplastic synthetic material, bearing a second external contact,

positioning said second end wall so that said second external contact touches a cell contact within said jacket,

exerting a deforming pressure upon said second end wall thereby slightly displacing said rst end wall in the terminal portion of said jacket, said pressure being transmitted by way of said cell means in said jacket to the opposite end wall and arching said iirst end wall outward elastically,

applying heat and pressure to said second end wall,

welding the terminal portion of said jacket to the adjoining second end wall,

relieving said pressure from the top of said second end wall after cooling and solidifying of the weld, permitting the elastic return of said trst end wall to its original shape thereby producing a considerable contact pressure between the cell contacts and the external contacts embedded in the two end walls.

2. In a method, as claimed in claim 1, wherein said galvanic cell means is at least one galvanic cell.

3. In a method, as claimed in claim 1, wherein said galvanic cell means is a stack of abutting galvanic cells.

4. In a method of rendering galvanic cell means leakproof by encasing in a jacket of thermoplastic synthetic material closed at one end by an end wall bearing a rst cell contact; and placing thereon a second end wall;

with the aid of z a pressure ram, pressure means, cooling means, welding means, and heating means,

the steps comprising:

lowering said pressure ram,

applying pressure to said pressure ram by said pressure means,

heating said welding means,

positioning said welding means while heating in contact with said second end wall of said jacket,

Welding said second end wall to said jacket.

5. In a method, as claimed in claim 4, with the aid of; said pressure ram having a wedge, a supporting element, a welding mold, at least one pneumatic cylinder, a sliding wedge, a cooling medium duct, a heating body, and heat shield,

the steps comprising:

inserting said thermoplastic jacket into said supporting element,

lowering said pressure ram,

holding said pressure ram in position with the aid of said pneumatic cylinder,

permitting said sliding wedge to come in Contact with the wedge of said pressure ram,

restraining said wedge from moving,

applying pressure with the aid of said pneumatic cylinder,

placing said heating body on said Welding mold,

permitting said mold to absorb heat from said heating body,

moving said heating body downward while containing to heat,

positioning said heating body in contact with said second end wall of said jacket,

heating to a Welding temperature,

welding said second end wall,

permitting pressure to build up in said pneumatic cylinder, thereby lifting said heating body,

permitting cooling of said mold,

lifting said welding mold by the application of pressure in said pneumatic cylinder,

retracting said pressure ram,

retracting said sliding wedge,

removing said thermoplastic jacket from said supporting element.

References Cited UNITED STATES PATENTS 1,481,145 l/l924 Pepper 136-133 2,411,272 11/ 1946 Keller 136-133 3,449,171 6/1969 Knight 136-175 WINST ON A. DOUGLAS, Primary Examiner D. L. WALTON, Assistant Examiner 

